Glycerol glycosides represented by glucosylglycerol, galactosylglycerol and the like are known to exist in plants such as algae (Non-patent Document 1) and fermented foods such as sake, miso (soybean paste) and mirin (sweet cooking sake) (Patent Document 1). These glycerol glycosides are useful as precursors for synthesis of glyceroglycolipids, and their condensation with fatty acids by use of a catalyst such as an acid or an enzyme such as lipase enables synthesis of glyceroglycolipids. Further, these glycerol glycosides have water-retaining property by themselves, and are useful compounds effective for enhancing the stability of emulsions. In Patent Document 2, for example, galactosylglycerol has been substantiated to have water-retaining property and a stability-improving effect on emulsions, and examples of its application to skin cream and face lotion are disclosed.
As a process for obtaining a glycerol glycoside, (1) extraction from a plant or the-like which contains the glycerol glycoside, (2) hydrolysis of a glyceroglycolipid, (3) synthesis from a glycerol donor and a saccharide donor, or the like can be mentioned. When the process (1) is used, the glycerol glycoside exists only in a very little amount in the plant, so that a large amount of plant is required to obtain only a small amount of sample and its purification is complex and requires substantial labor. As the process (2), for example, can be mentioned the process disclosed in Patent Document 3 in which a glycerol glycoside is produced by hydrolyzing naturally-occurring glyceroglycolipids in the presence of an ion-exchange resin. In this process, the glyceroglycolipids used as raw materials are mostly derived from animals or plants, and moreover, the contents of glyceroglycolipids in animals or plants are low. Accordingly, these glyceroglycolipids are very costly, and are not suited for industrial use. The process (3) is widely used to directly glycosidate not only glycerol but also various aglycones. Reactions making use of an acid catalyst, a glycosyltransferase or the like are known. For example, Patent Document 4, Patent Document 5 and Patent Document 6 disclose processes for producing galactosylglycerol by causing various glycosyltransferases to act on a galactose donor such as lactose and a glycerol donor. However, the glycosidation of a polyhydric alcohol such as glycerol is expected to form a mixture of galactosylglycerol glycosidated at the 1-hydroxyl group of glycerol, galactosylglycerol glycosidated at the 2-hydroxyl group of glycerol, and galactosylglycerol glycosidated at plural hydroxyl groups of glycerol, and therefore, selective synthesis is difficult. As many of naturally-existing glyceroglycolipids have a structure in which a saccharide is bonded to the 1-hydroxyl group of glycerol, it is desired to selectively obtain a glycerol glycoside in which the 1-hydroxyl group of glycerol is glycosidated in view of its use as a precursor of a glyceroglycolipid.
As a still further process, a reaction that produces glucosylglycerol from allyl glucoside via its epoxy derivative is disclosed in Non-patent Document 3. However, this process includes many reaction steps and is not considered to be a convenient process. Moreover, Patent Document 7 discloses use of a glyceroglycolipid analogue, which has been substituted at a hydroxyl group in the glycerol moiety and is similar to a glycerol glycoside, as an antiplaque agent. In this prior art document, the glyceroglycolipid is synthesized by a complex, multi-step synthesis process.
Non-patent Document 1: Carbohydr. Res. 73, 193-202, 1979
Non-patent Document 2: J. Am. Chem. Soc., 76, 2221, 1954
Non-patent Document 3: J. Carbohydr. Chem. 17(6), 937-968,
Patent Document 1: JP-A-11-222496
Patent Document 2: JP-A-09-38478
Patent Document 3: JP-B-05-25880
Patent Document 4: JP-B-2527345
Patent Document 5: JP-A-2002-218993
Patent Document 6: JP-A-09-140393
Patent Document 7: JP-A-06-80545